Investigation properties of high frequency welded steel pipes for natural gas transportation made of X60 steel

Abstract

The basic idea in this research work is to check the prescribed quality requirement of steel pipes welded by the implementation of the high-frequency contact welding process (HFCW). These pipes are intended for natural gas transportation. As a raw material for pipe production, X60M steel coils with a thickness of 6.5 mm were used. The outer diameter of the pipe is Φ508, and the length is 12000 mm. A preliminary welding procedure is given based on personal experience and technical knowledge. Special attention was paid to the most important welding parameters: current frequency, voltage, and welding speed. After performing the welding, additional heat treatment (normalization) of the welded pipes (joints) was performed at the temperature of 9000°C. In order to confirm proposed welding technology, complex investigations were performed. As the first chemical analysis of the base metal was performed. Nondestructive testing encompasses visual inspection and ultrasound testing of pipes, while destructive testing consists of tensile testing, bend testing, and hardness measurement. Besides, for analysis of the micro- and macrostructure of the welded joint, a metallographic investigation was made. Hydrostatic and flattening tests as technological investigations were performed too. Carried-out investigations confirmed that produced pipes with predicted welding parameters completely fulfilled standard requirements, and serial production of ordered pipes for natural gas transportation was realized.